This present invention relates generally to optical techniques. More particularly, the invention provides a method and structure for fabricating and controlling a steerable mirror. Merely by way of example, the invention has been applied to a steerable mirror featuring a reflective surface in the shape of an annulus as can be found in telescopes commonly referred to as Cassegrain telescopes. The method and structure can be applied to other applications as well such as air or space borne telescopes, laser systems, laser radar systems, and the like.
Conventional steerable mirrors have been used in a wide variety of applications. Certain applications include spatial chopping secondary mirrors on infrared telescopes, beam stabilization for laser communications and imaging, including motion compensation, and beam steering for directed energy systems. In these applications, angular steering ranges and rates can range between one to thirty (1–30) milliradians at tens to several hundred hertz.
FIG. 1 is a simplified schematic diagram of a conventional steerable mirror. A mirror 110 is mounted on a two-axis flexure 115, which in turn, is mounted on a support base 120. A plurality of force actuators 112, such as Lorenz force actuators, mounted in between the support base and the bottom (non-reflective) side of the mirror, enable the operator to adjust the tilt angle of the mirror in both the x-z and the y-z plane. Tilting in the x-z and y-z planes is sometimes referred to as a rotation of θy degrees around the y-axis and a rotation of θx degrees around the x-axis, respectively. In the conventional steering mirror illustrated in FIG. 1, inductive position sensors 125 are mounted on the support base and used to monitor the position of the mirror. There are many drawbacks in the conventional steering mirror illustrated in FIG. 1. The mirror surface is limited in a range of motion, which is undesirable. The limited range of angular motion is typically limited to +/−10 or 20 mrad, precluding the mirror from being used in applications that require larger ranges of motion. Moreover, the range of motion is limited in the direction perpendicular to the support base. Additionally, the flexure and the mirror in FIG. 1 are coupled so that the center of rotation is aligned with the center of mass. The hole bored in the lower surface of the mirror to provide for this flexure mounting location weakens the mirror substrate. Weakening of the mirror substrate may result in undesirable deformations of the mirror surface, adversely impacting optical and structural performance. Therefore, there is a need in the art for an improved steerable mirror system.
These and other objects and features of the present invention and the manner of obtaining them will become apparent to those skilled in the art, and the invention itself will be best understood by reference to the following detailed description read in conjunction with the accompanying drawings.